1. Field of the Invention
The present invention relates to a liquid ejection head to be mounted in a liquid ejection apparatus that ejects liquid such as ink for recording operations.
2. Description of the Related Art
Ejection ports of liquid ejection heads that eject liquid such as ink for high quality image recordings on recording media are required to be downsized to micro dimensions and highly densely arranged. U.S. Pat. No. 7,585,616 discloses a configuration of a liquid ejection head having very small and highly densely arranged ink ejection ports. The disclosed liquid ejection head includes ink ejection ports, liquid channels through which ink is supplied from an ink tank, recesses (lenses) formed on the ink ejection surface of the liquid ejection head and centered at the respective ink ejection ports and ejection sections that respectively link the liquid channels and the corresponding ink ejection ports. Thus, the liquid ejection head includes a plurality of ink ejection ports and each of the ink ejection ports is combined with a liquid channel, a recess and an ejection section that are formed for the ink ejection port.
According to the invention disclosed in the above-cited U.S. Pat. No. 7,585,616, liquid channels are formed in a channel forming member that is bonded to a substrate and ejection sections, each having a tapered profile over the whole circumference thereof, are provided so as to communicate with respective ink ejection ports that are formed on the surface of the liquid ejection head. The substrate and the channel forming member are bonded to each other. More specifically, the channel forming member is bonded to the substrate at the part thereof that is free from liquid channels. The ejection sections are formed with a tapered profile so that ink may be conveyed to the ink ejection ports with little energy. However, as the ejection sections that communicate with the respective ejection ports having a predetermined size are made to represent an entirely tapered profile, any two adjacently located liquid channels are separated from each other inevitably only by a small gap. As the gap separating two adjacently located liquid channels becomes small, the contact area of the substrate and the channel forming member becomes small to give rise to a problem that the adhesion of the channel forming member to the substrate consequently becomes less tight. When the channel forming member is made to adhere to the substrate less tightly, the channel forming member can be lifted from the substrate by the pressure applied to eject ink. Then, the ink flowing through a liquid channel can flow into neighboring liquid channels. As a result, the inks flowing through neighboring liquid channels can be mixed with each other. Additionally, when the channel forming member is peeled off from the substrate under pressure, there arises a situation where ink can no longer be ejected from the liquid ejection head.
Meanwhile, the refill frequency that represents the time period from an ink ejecting operation to the next ink ejecting operation is set to a high level for the purpose of raising the recording speed on a recording medium. As a high refill frequency is set, the number of times of ink ejection per unit time increases. Then, ink needs to be easily ejected from ejection ports. For the purpose of easy ink ejection, each of the ejection sections is made to represent a profile that is tapered toward the corresponding ejection port and hence the cross-sectional area of the ejection section is gradually decreased toward the ejection port. With this arrangement, ink can be ejected with little energy if compared with an arrangement where each of the ejection sections is made to represent a cylindrical profile. However, when the refill frequency is high and the resistance of the liquid channel against ink is small, the meniscus of ink at each of the ejection ports easily vibrates. Then, ink can easily spill out from the ejection port due to vibrations to give rise to a problem that the ink ejection surface of the liquid ejection head is wetted by spilled ink. To avoid this problem, a countermeasure of treating the ink ejection surface of the liquid ejection head is taken to make the surface able to easily absorb spilled ink. However, if ink spills onto the ink ejection surface in a large volume, all the spilled ink cannot be absorbed by the treated ink ejection surface and, consequently, the ink ejection surface of the liquid ejection head becomes wetted. Thus, a countermeasure of providing each ink ejection section with a recess for the purpose of preventing ink from spilling out onto the ink ejection surface of the liquid ejection head is also taken. However, if the capacity of the recesses is small relative to the refill frequency, the recesses cannot accommodate the ink overflowing from the ejection sections and ink can spill out from the recesses to consequently wet the ink ejection surface of the liquid ejection head.